Spark-plug.



I. M. HOFFMANN.

SPARK PLUG.

APPLICATION FILED APR. I8. I9I7.

Patented 1mg. 14, 1917.

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` .rosnrn 1a. Herrmann, or BROOKLYN, NEW Yoan.y

` eraan-PLUG.

To all; lwhom t may conce-fm:

Be it known that I, JOSEPH M. HOFFMANN, a citizen of the f United States, residing at- Brooklyn, in the count-y of Kings and State of New York, have invented certain new and 'useful' Improvements lin Spark-Plugs, of

which the following is a full, clear, and exact specification.

This invention relates to spark plugs, and has for its object to improve the construction of the electrodes so as to prevent the formation of carbon thereon to an extent which will interfere with the constant arc or spark.

Another object is to prevent improper sparking at other points than at the ends of the electrodes. A further object is to provide for adjusting one electrode toward and away from the other electrode in order to secure the most eicient length of spark. Other objects will appear as the description proceeds.

The invention will be first hereinafter described in connection with the accompanying drawings and then more specifically de fined at the end of the description.

In the accompanying drawings, wherein similar'reference characters are used to designate corresponding parts throughout the several views:

Figure 1 is a central longitudinal section through a spark plug constructed substantially in accordance with this invention.

Fig. 2 is a plan view thereof, and

. Fig. 3 is a section on the line III-'III of 1 looking in the direction of the arrows.

The body or casingof the spark plug comprisesa lower tubular member 1 and an upper tubular member which are adjust-ably connected by screw threads 3 so as to clamp between them an annular flange 4 on the tubular insulating member 5. The joint between the members 1 and 2 is preferably packed, as at 6.

At the upper end of the insulating member 5, which extends well above t-he upper member 2 of the spark plug casing, there is fastened a binding post 9 in which the electrode 10 has screw-threaded engagement whereby thelattermay be adjusted axially by using a pair of pliers or a wrench on a flattened plug 11 at the upper end of the electrode 10. Said electrode extends through the central passage 7 of the insulating member 5., and near its lower end has screwthreaded engagement with a nut or collar 12 having an inclined upper face 13 bearing Y Specification of Letters latent.. .j Pggtentgd Aug. 14, 1917. Application le'd April 18, 191%'.

serial No. 162,351.

to a point below the lower end of the elec' trode 10,`so that it effectually prevents the formation of improper sparks between the sides of the electrode and inner walls of the lower member 1 of the casing.

The lower end of the elect-rode 10 has its outer marginal portion flattened, as at 14, while from its central portion a tapered lug 15 projects downwardly for some distance and terminates in a semi-spherical or rounded cavity 16 forming a circular knife edge 17 around the base of said tapered lug 15. The other electrode comprises a cross bar 18 having its ends fastened at diametrically opposite points to the lower end of the member 1 of the casing. At an intermediate point on the cross bar 18 there is formed an upwardly extending lug 19 having a .rounded convex head arranged in line with the lower end of the electrode 10. The head of the lug 19 is preferably of greater diameter than the base of the tapered lug 15, and in operation a circular spark is formed all around the knife edge 17 between said tapered lug 15 onthe electrode 10 and the headed lug 19 on the elect-rode 18.

Because of the construction or formation of the electrodes, as shown and described, there is' little danger or chance of carbon forming thereon to an extent sufficient to interfere with the proper formation of the arc or spark. It is difiicult for carbon to collect on the knife edge 17, but if it should possibly occur, the cavity 16 would still be clear to form the arc, or if the lmife -edge 17 and cavity 16 should bot-h become bridged with carbon, the are may still be formed between the flattened marginal portion 14 at the end of the electrode 10, and the hea-ded lug 19 on the electrode 18.

'Having thus described my inventiomwhat I claim as new and desire to secure by Letters Patent of the United States is:

1. In a spark plug, the combination with an electrode having a spark-forming lug, of another electrode having a flattened marginal portion at its sparkforming end, and a lug extending from the central portion of saidlspark-forming end of the second electrode and having a cavity forming an annular knife edge for the purpose specified.

2. In a spark plug, the combination with an electrode having a spark-forming lug, of

anotherelectrode having a attened'margin'al portion on its spark-forming end,l and a tapered lug projecting, from the central portion of the spark-formingqend of the second electrode.

` 3. In a spark plug, the combination with an electrode having a spark-forming lug, of another electrode having a attened marginal portion at its spark-forming end, and a tapered lug projecting from the central portion of said spark-forming end of the second electrode and having va cavity forming an annular knife edge :for the purpose specified.

lIny a spark plug, the combination with. `an electrode having a spark forming lug provided with a rounded convert head, of another electrode having a cavlty- 1n its spark-forming end forming an annular knife In testimony whereof I have signed my name to this specification.

JOSEPH M. HOFFMANN. 

